Heretofore, the pixel map memory size (PM) required to display an image Y scanlines long and X pixels wide with C color bits was: EQU (X pixels)(Y lines)(C color bits)=Pixel Memory Size EQU (X)(Y)(C)=PM.
The XY pixel area of the display image (a very large number of bits) was multiplied by the color requirement to produce an even greater bit requirement.
Walker U.S. Pat. No. 4,364,037 shows an XYC pixel memory map which contains only edge and color data of the faces forming the display image. Non-edge pixels between the face edges fill the bulk of the map, The non-edge portion of the map is maintained at "0"s (background code). During each interframe update, the entire memory map is reset to "0", and the next frame of edge-color data is loaded. The interframe update time is greatly reduced because only the edge data must be entered on a bit-by-bit basis.
Walker U.S. Pat. No. 4,317,114 shows an XYC pixel map in which grids, legends, and formats may be added by an XY overlay memory. In one embodiment, an XY pixel map was employed containing only edge data. Color was added by an XYC overlay memory.